The long term objective is to provide a better understanding of the role of magnesium (Mg) with and without fluoride (F) or carbonate (CO3) on the formation and stability of calcium phosphate (Ca-P)* phases of enamel, dentin, cementum and bone. Information from this study could be useful in formulating regimens for calculus control and remineralizing solutions for root caries. Specific aims include: (1) determine Mg distribution (a) in inorganic and organic phases of calcified tissues; (b) between normal and diseased enamel, dentin, bones; (2) define the correlation between Mg levels and (a) those of CO3, F, HPO4, Ca/P; and (b) physico-chemical properties (lattice parameters, crystallinity, dissolution properties, b- TCP/HA ratio after ignition) of biological and synthetic apatites (AP); (3) define the correlation between Mg levels in bones of mice and rats with: (a) age, (b) amount of intraoral injections of Mg and Mg+F; and (c) F supplementation; (4) determine the critical levels of Mg which will prevent the transformation of ACMP* to AP*; (5) determine the effect of CO3, F, HPO4 on the Mg-for-Ca substitution in AP* and in b-TCMP*; (6) to determine the synergistic or antagonistic effect of Mg with CO3, F, HPO4 or P2O7 on the formation and properties of synthetic AP; (7) determine the effect of Mg on the formation of Ca-P phases: (a) under conditions of constant composition, and (b) in gel systems; (7) investigate the transformation of Ca-P phases* in serum and in saliva; (8) determine the critical solution [Mg/Ca] ratio with and without F or which will affect the formation/transformation of Ca-P phases: (a) in solution and (b) in gel systems; (9) prove the non-existence of Mg-containing non-apatitic phases (dolomite, b-TCMP) in the mineral phases of teeth and bones; (10) study synthetic AP (with Mg and CO3) to explain (a) reported 'preferential loss of Mg and CO3 in caries, and (b) occurrence of b-TCMP in dentin but not in enamel caries. Biological materials (normal, carious, fluorotic human teeth; shark teeth; mice, rat, chick bones) and synthetic Ca-P* will be characterized by x-ray diffraction, infrared absorption, thermogravimetry, SEM/TEM, atomic absorption, chemical analyses and dissolution in acid bufer. Data generated will be analyzed for statistical validity. [*Ca-P phases: ACMP, Mg-substituted amorphous calcium phosphate; DCPD, dicalcium phosphate dihydrate; OCP, octacalcium phosphate; b-TCMP, Mg-substituted whitlockite; AP, non-stoichiometric apatite].